This invention relates to fluid-gauging systems and methods.
The invention is more particularly, but not exclusively, concerned with aircraft fuel-gauging systems.
Aircraft include fuel-gauging systems to measure the quantity of fuel present in the fuel tanks. There are usually several fuel tanks, often located in the wings, each tank usually having several sensors or probes to measure the height of fuel present. With knowledge of the shape of the tank and the height of fuel at several different locations, the system can compute the volume of fuel in each tank. The number of probes needed depends on the pitch and roll angles likely to be experienced by the aircraft during flight. The gauging probes may be of the capacitive kind, where the capacitance of the probe varies with height of fuel. Alternatively, the probes may be of the ultrasonic kind, where the height is calculated from time for a pulse of acoustic energy to travel from an acoustic transducer at the bottom of the probe to the fuel surface and back to the transducer after reflection from the fuel surface. These systems can provide a highly accurate indication of fuel quantity over a wide range of aircraft attitudes during flight. The fuel-gauging system is also used on the ground during refuelling in order to check on the quantity of fuel dispensed to the aircraft. Aircraft often also include a secondary, back-up fuel-gauging system of a simpler, less accurate, mechanical kind. This is used to provide additional evidence of fuel quantity if there is disagreement between the primary fuel-gauging system and the flow meter in a fuel tanker dispensing fuel to the aircraft on the ground.
It is undesirable to have to provide a secondary gauging system because of the additional cost and weight of such systems, and the difficulty of fitting such a system to modern composite wings. It is possible to provide a secondary electronic gauging system but the cost of the additional sensors makes this prohibitive in most cases. The additional weight is also a severe disadvantage.